Shape memory alloys (SMAs) are metallic alloys that may recover apparent permanent strains when they are heated above a certain temperature. SMAs have two stable states or phases; a hot or austenite state and a cold or martensite state. The temperatures at which the SMA changes states (i.e. its crystallographic structure) are a characteristic of the particular alloy. Selecting the material composition of the alloy and anneal temperatures of the alloy may be used to control the alloy's transition temperatures.
In the austenite state, the alloy is hard and rigid, while in the martensite state, the alloy is softer and flexible. In the martensite state, the SMA may be stretched or deformed by an external force. Upon heating, the SMA will return to its austenite state and contract or recover any reasonable stretch that was imposed on it. Thus, the SMA recovers with more force that was required to stretch it out. This exerted force upon contraction may be used to perform any number of tasks such as, but not limited to, turning a device on or off, opening or closing an object, or actuating a device or object.
HVAC systems provide air or another fluid to compartments, such as rooms for example. A diffuser may be provided at the system outlet to distribute, in a particular way, the air or other fluid entering the room. For example, the diffuser may have one or more blades to direct the flow of the air.
Due to the buoyancy effect of air (i.e. cold air will naturally sink and hot air will naturally rise), heating air and cooling air are preferably provided to a room in different patterns. When both heating and cooling air are provided to the room through a single diffuser, the ability to adjust the diffuser to provide different flow patterns is desirable. Some diffusers may be manually adjusted while other diffusers may sense supply air temperature and adjust the diffuser through the use of a powered control system, bimetallic strips, or wax motors.